POS0919 [18F] POSITRON EMISSION COMPUTED TOMOGRAPHY ([18F] FDG PET/CT) IS ABLE TO PREDICT ULTRASOUND-DEFINED REMISSION IN RHEUMATOID ARTHRITIS
Authors: C. Rinkin, C. Florane, C. Gérard, L. Seidel, C. Lamaye, R. Hustinx, M. Malaise, C. Ribbens, O. Malaise
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Assessing joint inflammation in rheumatoid arthritis (RA) is of high importance because associated with structural damage. In addition to clinical examination and ultrasound (US), joint inflammation can also be quantified by [18F] positron emission computed tomography ([18F] FDG PET/CT). Nowadays, PET/CT is widely used for cancer evaluation and systemic inflammation work-up and it can be used for opportunistic joint evaluation in RA patients. In addition, PET/CT allows a whole-body articular evaluation in one examination. We, and others, have previously demonstrated that PET/CT is significantly correlated with US parameters, but with a weak correlation coefficient. <h3>Objectives</h3> We investigated the ability of PET/CT to predict US-defined remission at the joint level and at the patient level. <h3>Methods</h3> 61 RA patients were included and underwent [18F] FDG PET/CT and US evaluations. For PET/CT, standardized uptake value (SUV) was determined on 22 joints (wrists, PIP and MCP of both hands). At the patient level, the maximum SUV (SUVmax), the number of PET positive joints (SUV&gt;0) and the sum of all SUVs (cumulative SUV) were evaluated. US evaluation included gray-scale and Power Doppler imaging, according to OMERACT. <h3>Results</h3> At the joint level, PET/CT activity (SUV) was significantly different when the joint was under US remission or not (OR 0.411, p&lt;0.0001 with remission defined as "no synovitis grade ≥ 2 with no PDI "). ROC-curves identified SUV thresholds to define joint remission with a high predictive positive value (95.2; confidence interval (CI): 93.8-96.4), but with low negative predictive value (28.9; CI: 21.7-36.8). When wrists, MCP and PIP were evaluated separately, AUC was higher for wrists. Predictive positive value was high for each sub-type (93.4, 94.2, 96.3% respectively). Negative predictive value was low for MCP and PIP (34.0 and 22.2%) but better for wrist (71.4%). At the patient level, SUVmax was significantly different when the patient was under US remission or not (p=0.0023 with remission defined as "no synovitis grade ≥ 2, no PDI, no tenosynovitis"). Cumulative SUV was also different (p=0.045) while there was no difference for the number of PET-positive joints. SUVmax threshold was determined with ROC-curves and demonstrated a high negative predictive value for determining US remission (92.9, CI: 66.1-99.2), while the positive predictive value was lower (67.4, CI: 52.0-80.5). For cumulative SUV threshold, negative and predictive value for determining US-defined remission were 73.1 and 73.5 respectively. <h3>Conclusion</h3> PET/CT is able to predict US-defined remission in RA patients. In addition to its well-known role in cancer evaluation and systemic inflammation work-up, PET/CT is also a promising tool in RA metrology. When considering US remission at the joint level, the predictive positive value is high, while the predictive negative value is better when predicting US remission at the patient level. Among PET/CT parameters, the maximum SUV (SUVmax) and the cumulative SUV exhibit the highest performances to predict US remission. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.